The studies address aspects of the regulation of hematopoiesis with specific emphasis on the in vitro assessment of hormonal and cellular interactions. Specific studies are outlined in three general areas: 1. Hormonal and cellular interactions in hematopoietic cell growth. We will study the influence of platelet derived growth factor (PDGF) and growth factors released by marrow stromal cells on erythroid, granulocyte/macrophage, and megakaryocytic colony formation in man. The target cell for these interactions (early or late erythroid progenitor) and potential accessory cells will be defined. Inhibitors of in vitro hematopoieses in chronic renal failure (CRF) will be assessed and correlated with the extent of uremia and anemia in patients with a wide range in renal function. We will also treat some patients with CRF with erythropoietin (Ep)-rich human plasma to quantitatively assess their response. Inhibitors found to be active will be partially isolated and a more detailed study of their effect on hematopoietic cell growth carried out employing human and murine hematopoietic cell lines. 2. Ep purification. Increased amounts of human urinary Ep will be purified, antibodies raised to the amino terminal sequences as well as to purified hormone, and immunoaffinity chromatography performed to increase recoveries of active hormone. mRNA from anemic baboon kidney has been extracted and a cDNA library prepared. Various strategies will be employed to label the purified hormone, prepare a radioimmunoassay, and identify clones of genomic material containing Ep-coding sequences. 3. Clonal disorders of the hematopoietic multipotent stem cell. We will continue to use glucose-6-phosphate dehydrogenase (G6PD) as a marker focusing on patients with essential thrombocytosis and employing the human megakaryocyte colony-forming cell assay as well as an assay for a multipotent progenitor.